Millimetre-Wave Superconducting Quantum Amplifiers for Radio Astronomy

高灵敏度的微弱信号的放大几乎完全是用高电子迁移率晶体管（HEMT）放大器实现的。它们是天文学、量子计算、地球观测和低温物理等最灵敏仪器的组成部分。然而，HEMT放大器有根本的缺点。灵敏度仍然超出了可以达到的水平，接近量子极限水平。它们非常耗电，需要大量的散热，并且在更高的频率下，噪声温度和带宽都会迅速恶化。因此，人们对开发一种具有量子限制噪声性能、宽带高增益、超低功耗、能够在毫米和亚毫米波长范围内工作的新型放大器技术有着浓厚的兴趣。新兴的超导参数放大器技术有可能满足所有这些要求。放大是通过改变设备电抗，通过一个强大的“泵”波，将允许功率从强泵转移到弱信号实现的。由于该过程完全依赖于超导非线性反应响应，耗散非常小，因此可以达到量子极限。它们体积小，坚固耐用，用途广泛，制造成品率高。在这一领域发表的大多数工作都描述了只能在微波频率下工作的spa。该博士项目旨在开发一种宽带SPA，该SPA将在毫米波波段工作，作为为无线电，毫米和亚毫米天文接收器开发的量子混频器的前置放大器。该装置的研制将对毫米及亚毫米天文和b模宇宙微波背景（CMB）实验产生巨大影响，因为在混频器或第一级探测器前添加高增益的量子噪声限制SPA将使接收机灵敏度提高一个数量级以上。在这个项目中，学生将学习理论背景和仿真技术来模拟SPA，同时学习使用商业电磁学软件来设计放大器。学生将有机会使用最先进的无尘室设施参与设备的制造，可以在牛津大学，也可以与我们的其他合作者一起。学生还将学习如何使用亚开尔文低温系统和其他实验技术来测量放大器的性能。特别是，学生将研究毫米波频率下SPA的工作，以及它们的性能对物理温度和用于形成SPA的超导材料的依赖。最后，学生将把放大器集成到现有的毫米波天文接收机中，并评估对接收机性能的影响。这个项目属于天文仪器研究领域。

Amplification of weak signals with high sensitivity is almost exclusively achieved using high electron mobility transistor (HEMT) amplifiers. They are an integral part of the most highly-sensitive instruments for astronomy, quantum computing, Earth observation and low-temperature physics. HEMT amplifiers however have fundamental drawbacks. The sensitivity is still beyond what can be achieved, to approach the quantum limited level. They are power hungry, requiring substantial heat dissipation, and both the noise temperature and bandwidth deteriorate rapidly at higher frequencies. There is therefore an intense interest for developing a new amplifier technology with quantum-limited noise performance, high gain over wide bandwidths, ultra-low power dissipation and capable to operate in the millimetre (mm) and sub-mm wavelength regime. The emerging technology of superconducting parametric amplifiers (SPAs) has the potential to achieve all these requirements. Amplification is achieved by varying the device reactance via a strong 'pump' wave that would allow power transfer from the strong pump to the weak signal. Because the process relies purely on superconducting nonlinear reactive response, dissipation is exceedingly small, therefore allowing the quantum limit to be achieved. They are also small in size, robust and very versatile with high fabrication yield. Most published work in this area described SPAs that could operate only at microwave frequencies. This PhD project aims to develop a wideband SPA that would operate at millimetre wave regime as pre-amplifier for the quantum mixers developed for radio, mm and sub-mm astronomical receivers. The development of such a device will have a huge impact in mm & sub-mm astronomy & B-mode Cosmic Microwave Background (CMB) experiments, as a quantum-noise limited SPA with high gain before the mixer or the first stage detector will improve the receiver sensitivity by more than an order of magnitude. In this project, the student will be studying the theoretical background and simulation technique to model the SPA, along with learning to use commercial electromagnetism software to design the amplifiers. The student will have the chance to get involve in the fabrication of the devices using state-of-the-art clean room facilities, either here in Oxford, or with our other collaborators. The student will also learn how to use sub-Kelvin cryogenics system and other experimental techniques, for measuring the performance of the amplifiers. In particular, the student will investigate the operation of the SPA at mm-wave frequencies, and their performance dependence on the physical temperature and the superconducting materials used to form the SPAs. Finally, the student will integrate the amplifier into an existing mm-wave astronomical receiver and assess the impact on the receiver performance.This project falls within the astronomical instrumentation research area.